1. Field of the Invention
The present invention relates to high power lamps. More particularly, the present invention relates to cooling high power lamps and the use of such lamps in display systems.
2. Description of Related Art
A high power light source required for industrial or commercial applications typically has higher output than incandescent and fluorescent lamps. One type of lamp, known as a high intensity discharge (HID) lamp is constructed of a glass (or other thermally insulative) envelope that contains electrodes and a fill, typically mercury. The mercury vaporizes and becomes a light emitting gas when the lamp is operated. U.S. Pat. Nos. 5,404,076, entitled "Lamp Including Sulfur," and 5,606,220, entitled "Visible Lamp Including Selenium or Sulfur," both issued to Dolan et al., incorporated by reference herein in their entirety, disclose electrodeless HID lamps. These lamps include a bulb that uses a solid sulfur or selenium, or compounds of these elements, fill at a pressure at least as high as one atmosphere. These lamps are constructed with excitation sources and excitation structures (e.g., electrodes or microwave waveguides) adjacent the glass envelope. With microwave excitation, the fill in Dolan is excited to a plasma state at a power density in excess of 50 watts per cubic centimeter. Another lamp disclosed in Dolan includes electrodes and uses a similar fill at a pressure at least as high as one atmosphere. The fill in this lamp is excited using radio frequency (rf) excitation at a power density of at least 60 watts per cubic centimeter instead of using microwave energy. These lamps can also be operated at other pressures and power densities. Moreover, the lamp emission spectrum can be tailored by using additive materials in the fill, such as metal halides.
Prior, co-owned U.S. Pat. application Ser. No. 08/747,190, now U.S. Pat. No. 5,833,360, filed Nov. 12, 1996, by Richard M. Knox, Dale S. Walker, and William Burton Mercer, entitled "High Efficiency Lamp Apparatus for Producing a Beam of Polarized Light," incorporated by reference herein in its entirety, discloses a high efficiency lamp that produces polarized light. The lamp allows light of a preferred polarization and of preferred wavelengths to pass that is produced by an excited fill. However, the lamp redirects light of non-preferred polarizations and non-preferred (i.e., off-spectral) wavelengths as reflected light back to the light source. The reflected light is used to "optically pump" the fill by reabsorption for re-emission in the preferred polarization and at the preferred wavelengths. The preferred wavelengths are redshifted from the redirected (off-spectral) wavelengths.
Generally, these lamps or light sources generate much thermal energy while forming and maintaining the fill in the plasma state. The thermal energy can lead to high temperatures. Exposure of the lamp to high temperatures over an extended period of time can degrade the bulb and possibly the performance of electronics for powering the lamp. A cooling system is, therefore, needed. The aforementioned U.S. Pat. Nos. 5,404,076 and 5,606,220 disclose the use of compressed air jets or streams directed at the lamp to provide the necessary cooling while the bulb is spun or rotated in the jets. Air jets and a compressor, however, can increase the cost and complexity of the lamp.
The present invention is directed to overcoming or reducing one or more of the foregoing problems and other shortcomings.